1. Field
The following description relates to a battery management system, a method of removing a battery polarization voltage, and a method of estimating a battery charge state.
2. Description of Related Art
Recently, the European Union has decided upon a plan to expand the percentage of renewable energy, from among all electric power sources, up to 20% by the year 2020 and 50% by the year 2050. The United States of America is also planning to carry out Renewable Portfolio Standards (RPS). In a situation where renewable energy increases from less than 5% in today's energy use to be up to 30 to 40% in the future, power systems should be prepared for these new changes.
It is not easy to control the amount of generation of renewable energy. This is because the amount of generation of renewable energy varies according to natural conditions, such as solar light, wind power, and wave power. Research is being done on a scheme that is capable of overcoming degradation in power quality of a power system and a mismatch between production and consumption times, which can be generated due to a shift in renewable energy generation. Power quality is evaluated on the basis of voltage and frequency. If the supply quantity of renewable energy does not coincide with the demand quantity of renewable energy in real time, abnormalities are generated in voltage and frequency, thereby possibly deteriorating the power quality of all of the power systems.
A power storage system has been in the spotlight as an alternative that is capable of managing such a shift in renewable energy. This is because the power storage system can efficiently coordinate (or control) demand and supply by charging electricity when the amount of generation of renewable energy is high and discharging electricity when the consumption of renewable energy is high.
Power storage techniques include pumping-up power generation, compressed air energy storage (CAES), a flywheel technique, superconducting magnetic energy storage (SMES), rechargeable battery storage, and so on. The pumping-up power generation technique is a method of generating electricity by rotating a turbine by pumping water into a dam when excess electricity is available and discharging water from the dam when the amount of electricity is insufficient. The CAES technique is a method of generating electricity by compressing air in the ground or sea and then discharging the air as occasion demands. The flywheel technique is a method of generating electricity by rotating a top when excess electricity is available and rotating a power generator using the top when electricity is insufficient. The SMES technique is a method using a principle that current is stored in a superconducting coil having resistance of 0. The rechargeable battery is a battery that can be repeatedly charged and discharged, and has been used as an uninterruptible power supply (UPS) for temporarily supplying electricity upon a power failure. The rechargeable battery has recently been in the spotlight as an auxiliary power source for renewable energy.
The power storage system not only stores the generated power of the renewable energy to the large capacity rechargeable battery (hereinafter referred to as a battery) among a plurality of rechargeable batteries which are connected to each other, but is also in cooperation with a common grid to store the power of the common grid to the battery, or may supply the power stored in the battery to the common grid or the generated power of the renewable energy to the common grid. As described above, while the battery repeatedly charges and discharges the power in the power storage system, the battery executes an essential function of recovering a time of producing and consuming power that are important characteristics of the power storage system.
To improve an efficiency of the battery in which the charge and discharge of the battery is repeated, a state of charge (hereafter referred to as SOC) should be accurately estimated. The SOC of the battery may be estimated by measuring the voltage, however the voltage of the battery may not be accurately measured because of the polarization voltage that is generated in the process of charge and discharge. The SOC of the battery may be estimated by measuring the current, however there is a limitation in that an initial SOC of the battery must be recognized for the SOC estimation using the current measuring.
A method of more accurately estimating the SOC of the battery by quickly removing the polarization voltage generated according to the charge and discharge of the battery is needed.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.